MCP3909-I/SP Microchip Technology, MCP3909-I/SP Datasheet - Page 17

• Manufacturer Part Number: MCP3909-I/SP
• Description: Power Meter with SPI and Active Power Pulse Output & Internal Oscillator., -40C to +85C, 28-SPDIP, TUBE
• Manufacturer: Microchip Technology

4.2
The MCP3909 analog inputs can be connected directly
to the current and voltage transducers (such as shunts
or current transformers). Each input pin is protected by
specialized ESD structures that are certified to pass
4 kV HBM and 400V MM contact charge. These
structures also allow up to ±6V continuous voltage to
be present at their inputs without the risk of permanent
damage.
Both channels have fully differential voltage inputs for
better noise performance. The absolute voltage at each
pin relative to A
range during operation in order to ensure the measure-
ment error performance. The common-mode signals
should be adapted to respect both the previous
conditions and the differential input voltage range. For
best performance, the common-mode signals should
be referenced to A
The current channel comprises a PGA on the front-end
to allow for smaller signals to be measured without
additional
differential voltage specified on Channel 0 is equal to
±470 mV/Gain (see
voltage specified on Channel 1 is equal to ±660 mV.
TABLE 4-1:
4.3
The ADCs used in the MCP3909 for both current and
voltage channel measurements are delta-sigma ADCs.
They comprise a second-order, delta-sigma modulator
using a multi-bit DAC and a third-order SINC filter. The
delta-sigma architecture is very appropriate for the
applications targeted by the MCP3909 because it is a
waveform-oriented converter architecture that can offer
both high linearity and low distortion performance
throughout a wide input dynamic range. It also creates
minimal requirements for the anti-aliasing filter design.
The multi-bit architecture used in the ADC minimizes
quantization noise at the output of the converters
without disturbing the linearity.
Both ADCs have a 16-bit resolution, allowing wide input
dynamic range sensing. The oversampling ratio of both
converters is 64. Both converters are continuously
converting during normal operation. When the MCLR
pin is low, both converters will be in Reset and output
code 0x0000h. If the voltage at the inputs of the ADC is
larger than the specified range, the linearity is no longer
specified. However, the converters will continue to
© 2006 Microchip Technology Inc.
G1
0
0
1
1
Analog Inputs
16-Bit Delta-Sigma A/D Converters
signal
G0
0
1
0
1
GND
GAIN SELECTIONS
GND
should be maintained in the ±1V
Table
conditioning.
CH0 Gain
.
16
1
2
8
4-1). The maximum peak
The
CH0 Voltage
Maximum
±470 mV
±235 mV
±60 mV
±30 mV
maximum
produce output codes until their saturation point is
reached. The DC saturation point is around 700 mV for
Channel 0 and 1V for Channel 1, using internal voltage
reference. The output code will be locked past the
saturation point to the maximum output code.
The clocking signals for the ADCs are equally
distributed between the two channels in order to
minimize phase delays to less than 1 MCLK period
(see Section 3.2 “High-Pass Filter Input Logic Pin
(HPF)”). The SINC filters main notch is positioned at
MCLK/256 (14 kHz with MCLK = 3.58 MHz), allowing
the user to be able to measure wide harmonic content
on either channel. The data ready signals used for
synchronization of the part with a MCU will come at a
rate of MCLK/256 and a pipeline delay of 3 data readys
is required to settle the SINC 3rd order digital filter. The
magnitude response of the SINC filter is shown in
Figure
FIGURE 4-2:
Response (MCLK = 3.58 MHz).
4.4
The MCP3909 contains an internal voltage reference
source specially designed to minimize drift over
temperature. This internal V
voltage to both current and voltage channels ADCs.
The typical value of this voltage reference is 2.4V
±100 mV. The internal reference has a very low typical
temperature coefficient of ±15 ppm/°C, allowing the
output frequencies to have minimal variation with
respect to temperature since they are proportional to
(1/V
The output pin for the voltage reference is REFIN/OUT.
Appropriate bypass capacitors must be connected to
the REFIN/OUT pin for proper operation (see
Section 6.0
voltage reference source impedance is typically 4 kΩ,
which enables this voltage reference to be overdriven
by an external voltage reference source.
If an external voltage reference source is connected to
the REFIN/OUT pin, the external voltage will be used
as the reference for both current and voltage channel
ADCs. The voltage across the source resistor will then
REF
-100
-120
4-2.
-20
-40
-60
-80
)².
0
Ultra-Low Drift V
0
“Applications
5
SINC Filter Magnitude
10
Frequency (kHz)
15
MCP3909
REF
REF
Information”).
supplies reference
20
DS22025A-page 17
25
30
The